Former MP Oona King has pledged her support for Ken Livingstone in his fight to win back the London mayoralty after he soundly beat her for the Labour candidacy to take on Boris Johnson.
Mr Livingstone, whose two previous terms as mayor saw him open a rift with the Jewish community, will challenge the Tory incumbent in 2012.
Ms King lost her Bethnal Green and Bow parliamentary seat to George Galloway, following an acrimonious campaign in 2005.
Since then she had worked as a Downing Street adviser to former Prime Minister Gordon Brown.
Following her defeat by Mr Livingstone, announced last Friday, Ms King said: "Now we must turn our attention to the real fight - the wasted mayoralty and lack of vision of Boris Johnson. Ken Livingstone is a formidable politician who has never given up the fight. I am sure he will battle for London, as he always has, and we must give him our support as he does so.
"All of us must do our best to make sure Ken Livingstone is the next Mayor of London. And no one wants to see Ken defeat Boris Johnson more than I do."
Ms King has not ruled out running again for mayor in the 2016 election, but is now expected to return to her job as Head of Diversity at Channel Four.
Daughter of a Jewish mother and a black father, 42-year-old Ms King had earlier praised the "fantastic support" she received from the Jewish community in her battle with Mr Livingstone.
Jewish donors to her campaign included private equity millionaire Sir Ronald Cohen, who gave £7,000, and historian Simon Schama and YouGov pollster Peter Kellner who each donated £2,000.
But Ms King, who signed Jews for Justice for Palestinians' founding statement, struggled to gain widespread support from the community. Jewish voters in the capital are expected to back Mr Johnson for a second term. Since becoming mayor in 2008, he has been a regular attendee at community dinners and fundraising events.
Mr Livingstone's controversial previous stint running London included his welcome to radical Islamic cleric Yusuf al-Qaradawi and comparison of a Jewish journalist to a concentration camp guard.
Meanwhile, former Liberal Democrat MP Susan Kramer has announced she will stand for the party's presidency.
Ms Kramer, the daughter of a Hungarian Holocaust survivor, lost her Richmond Park seat to Tory Zac Goldsmith in May's election.
A former Citibank vice-president, she has previously said her Jewish roots give her an "appreciation and understanding of the importance of human rights and freedoms".
Hate discussed on the Labour fringe
A range of fringe events covering issues of Jewish and Israel interest took place at the Labour Party conference in Manchester this week.
On Monday night, MPs Jim Murphy and Tristram Hunt were due to be among the speakers at a Holocaust Educational Trust debate tackling Nazi analogies.
The event, hosted by HET chief executive Karen Pollock, also featured JC columnists Jonathan Freedland and David Aaronovitch.
The following night, Labour Friends of Israel held its annual party conference reception. Newly elected Labour leader Ed Miliband was expected to speak at the event.
The Parliamentary Committee Against Antisemitism Foundation hosted MPs John Mann and Margaret Hodge at a lunch session on Tuesday.
The New Statesman backed an event discussing aid and Gaza in partnership with the Medical Aid for Palestinians charity.